A capacitor is a passive two-terminal electronic component that stores electrical energy in an electric field. The effect of a capacitor is known as capacitance. While some capacitance exists between any two electrically charged conductors in proximity in a circuit, a capacitor is a component designed to add capacitance to a circuit. Most capacitors contain at least two electrical conductors often in the form of metallic plates or surfaces separated by a dielectric medium. The nonconducting dielectric acts to increase the capacitor's charge capacity. Capacitive elements, which include capacitors, typically present linear characteristics between stored charge and terminal voltages. But the relation between charge and voltage may be nonlinear for certain capacitive elements. In other words some capacitive elements may behave in a nonlinear fashion.
Automation, power efficiency, sensing resolution, complexity, etc., has led to systems that are more distributed. For example, integrated circuits can be partitioned by power domains, and power provided to these domains are gated for power savings. Other distributive systems include independent and remotely located units, or multiple cores. There are also systems with multiple power supplies. Distributive systems may contain multiple capacitive loads. A capacitive load can be seen as one or more interconnected capacitive elements. Distributive capacitive loads can present problems (e.g., power overload, data corruption, etc.) during power up or power down. An uncontrolled power down of, for example, a system with multiple power supplies that drive respective capacitive loads, may result in structural damage.
An example distributive system is depicted in FIG. 1 to illustrate damage that can occur to power supplies when capacitive loads are not properly discharged during a power down operation. FIG. 1 shows a multiple power supply system 100 that includes a pair of voltage regulators 102 and 104 that provide power to respective subsystems, each of which can be characterized as having a capacitive load. In FIG. 1, the capacitive loads are designated C1 and C2, respectively. Coupling capacitor C0, connected to V1 and V2 is part of the complex load of the regulators, together with respective capacitive loads C1 and C2. Each of the capacitive loads C1 and C2 may be linear or nonlinear. In the illustrated example voltage regulator 102 drives its subsystem, and hence its capacitive load C1, to a negative voltage V1. In contrast, voltage regulator 104 drives its subsystem, and hence its capacitive load C2 to a positive voltage V2. Voltage regulators 102 and 104 may be powered down at the same time. When this happens, node 106 may suddenly be driven to a negative voltage via coupling capacitor C0. This negative voltage on node 106 may damage one or more components of voltage regulator 104 and render it permanently inoperable.
The use of the same reference symbols in different drawings indicates similar or identical items.